Looking at it from a general perspective that has less to do with games themselves; I would say huge parts of the Assassins Creed games due to the accuracy they often have had with depicting historic architecture and such. ~~Heck, they used the games model of the Notre Dame in its reconstruction.~~ EDIT: [So I just looked this up and apparently it's just a nice story that has stuck. But the actual model was never used.]
From a more game-focused perspective, there are some real gems in there too (especially the Ezio-Series). Tho that quality has sadly not kept.